Sylvester Stallone has described how he suffered one of his most-serious injuries to date as he shot The Expendables 3.

And the 68-year-old action man, best known for playing Rocky and Rambo, joked that the severity of the injuries was related to the quality of his films.

Sly sustained a back injury - a "back blast", which needed surgery - as he filmed action scenes for the third instalment of The Expendables, reprising his role as leader Barney Ross, one of a number of mishaps for the stars.

He said: "I grade the quality of a film by the intensity of the injuries. When I shot Stop! Or My Mom Will Shoot, I never got hurt.

"Through Rambo and The Expendables, I break my neck and my spine and I dislocate both shoulders. In this one here, I end up really taking a fall on my back and had some metal put in there, so if you hear any squeaking, it's not my shoes but my back. But I'm getting better."

Stallone was joined by co-stars including Jason Statham, Wesley Snipes, Antonio Banderas and Kellan Lutz ahead of the film's world premiere in London tonight.

"I was injured in my first take but I went through the whole movie without saying anything because I didn't want them to think I was just getting older," the 53-year-old said.

"I got a pain in my right knee, from running up the roof to the helicopter. Now it's gone but it stayed there for a couple of months."

His co-star Stallone joked: "You got a pain in the knee? I wake up like that for breakfast. It's like a weird sporting event. You know you're going to get injured. Everyone shows up really fit on the first day and it goes downhill from there."

Sly also quipped about how Statham's (Lee Christmas) near-death experience was partly his fault.

"Jason actually fought death in the midst of the Black Sea. He's very modest about it but he drove a five-tonne truck 60 feet down into black mud because I cut the brake line," he said, laughing. "No one knows that, I wasn't meant to reveal that."

Snipes, 52, makes his big-screen comeback in the film, as Doc Death, following his release from prison in 2013 after serving more than two years for tax evasion.

"I loved it. These are the best players. I respect them. I've never played a real team sport before so this is the closest I've gotten," he said.

The Expendables 3 sees Harrison Ford and Mel Gibson as well a younger generation of actors such as MMA (mixed martial arts) fighter Ronda Rousey and boxing champion Victor Ortiz joining the team, which already includes action stars such as Dolph Lundgren, Terry Crews and Arnold Schwarzenegger.

Stallone also confessed action stars like him are "the hardest characters to sell" to other men.